add readme for content-type bypass and input validation

input_validation/README.md

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+# Client side validation bypass
+
+## How We Found It
+On the home page, there is a link to a survey page. this page has a list of subject, an average score and a number of vote. We can give a grade between 0 and 10.  
+But what if we change in the html page, the value of a score and put something bigger than 10, can we put a grade of 1000 ?  
+Yes we can, and we get a flag.
+
+## Utility of It
+This allows an attacker to:
+    - Submit invalid or malicious data (e.g., score > 10).
+    - Manipulate application logic (e.g., gain unfair advantage or retrieve flags).
+    - Potentially exploit further vulnerabilities if the data is used insecurely elsewhere (e.g., SQL injection, XSS).
+
+
+## How Can We Patch It
+    - Validate all input on the server side regardless of client-side checks.
+    - Enforce boundaries (e.g., score must be between 0 and 10) on the backend.
+    - Use a schema validation library or built-in mechanisms to reject bad data.
+    - Never trust client-side data blindly — browsers can be manipulated.